Brown Bear Den Habitat and Winter Recreation in South-Central Alaska

ABSTRACT Increasing demand for backcountry recreation opportunities during winter (e.g., snowshoeing, helicopter-assisted skiing, snowmobiling) in steep, high-elevation terrain has elevated concern about disturbance to brown bears (Ursus arctos) denning on the Kenai Peninsula, Alaska, USA. To help identify areas where such conflicts might occur, we developed a spatially explicit model to predict potential den habitat. The model indicated brown bears selected locations for den sites with steep slopes, away from roads and trails. Den sites were associated with habitat high in elevation and away from potential human contact. We then compared areas with the highest probability of providing den habitat with patterns of snowmobile and nonmotorized recreation on a portion of the Kenai Peninsula. We found limited overlap between the 2 recreation activities and potential den habitat for brown bears. At the landscape scale, however, backcountry skiing overlapped more high-quality den habitat than did snowmobile riding. Our results may be used by land management agencies to identify potential conflict sites and to minimize the potential effects of recreation activities on brown bears in dens.     

Biological and Statistical Errors Make Inferences Circumspect: Response to Bender and Weisenberger

ABSTRACT Bender and Weisenberger (2005) reported that desert bighorn sheep (Ovis canadensis) on San Andres National Wildlife Refuge (SANWR), New Mexico, USA, were primarily limited by rainfall. However, they failed to mention, or were unaware, that persistent long-term predator control was used to enhance population growth at SANWR. Additionally, lamb:female ratios were collected throughout the year, rather than dates typically associated with assessing recruitment, and therefore influence of precipitation on lamb recruitment was unknown. Finally, model predictions forwarded by Bender and Weisenberger (2005), that carrying capacity of SANWR is zero when annual rainfall is <28.2 cm, were not supported by data, nor were their model results properly interpreted. The coefficient of determination value of 88.9% for the relationship between population size and current year's precipitation was primarily a function of serial correlation between successive years in population data, with current year's precipitation accounting for only 3.8% of this value. This suggests that precipitation was a weak predictor of population increase. These errors in concert make biological inferences reported in Bender and Weisenberger (2005) of limited value.     

The Evolution of Avian Senescence Patterns: Implications for Understanding Primary Aging Processes

SYNOPSIS. The long life spans of birds relative to those ofmammals are intriguing to biogerontologists, particularly inlight of birds' high body temperatures, high blood glucose levels,and high metabolic rates—all of which should theoreticallyincrease their biochemical liability for rapid aging. The comparativelongevity of birds and other flying homeotherms is consistentwith evolutionary senescence theory, which posits that specieswith low mortality rates from predation or accident will bereleased from selection for rapid maturity and early reproduction,and will exhibit retarded aging. Comparative analyses of avianlife history parameters to date, although not as extensive asthose for mammals, broadly support an association between lowmortality rates, slow reproduction, and long lifespan. The diversityof bird life histories suggests the importance of developinga diversity of avian models for studies of aging mechanisms,both proximate and ultimate, and for using wild as well as domesticrepresentatives. Birds studied in the laboratory thus far showmany of the same manifestations of aging as mammals, includinghumans, and many ornithologists are beginning to document actuarialevidence consistent with aging in their study populations. Weencourage greater communication and collaboration among comparativegerontologists and ornithologists, in the hope that the studyof aging in birds will lead to an integrated understanding ofphysiological aging processes well grounded in an evolutionaryparadigm.     

Freezing tolerance and avoidance in high-elevation Hawaiian plants

Freezing resistance mechanisms were studied in five endemic Hawaiian species growing at high elevations on Haleakala volcano, Hawaii, where nocturnal subzero (°C) air temperatures frequently occur. Extracellular freezing occurred at around -5°C in leaves of Argyroxiphium sandwicense and Sophora chrysophylla, but these leaves can tolerate extracellular ice accumulation to -15°C and -12°C, respectively. Mucilage, which apparently acted as an ice nucleator, comprised 9 to 11% of the dry weight of leaf tissue in these two species. Leaves of Vaccinium reticulatum and Styphelia tameiameiae were also found to tolerate substantial extracellular freezing. Dubautia menziesii, on the other hand, exhibited the characteristics of permanent supercooling; a very rapid decline in liquid water content associated with simultaneous intracellular and extracellular freezing. However, in those species that tolerate extracellular freezing, the decline in liquid water content during freezing is relatively slow. Osmotic potential was lower at pre-dawn than at midday in four of the species studied. Nocturnal production of osmotically active solutes may have helped to prevent intracellular freeze dehydration as well as to provide non-colligative protection of cell membranes. Styphelia tameiameiae supercooled to -9·3°C and tolerated tissue freezing to below -15°C, a unique combination of physiological characteristics related to freezing. Tolerance of extracellular ice formation after considerable supercooling may have resulted from low tissue water content and a high degree of intracellular water binding in this species, as determined by nuclear magnetic resonance studies. The climate at high elevations in Hawaii is relatively unpredictable in terms of the duration of subzero temperatures and the lowest subzero temperature reached during the night. It appears that plants growing in this tropical alpine habitat have been under selective pressures for the evolution of freezing tolerance mechanisms.